Business Segment Reporting - Core Earnings (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of Operating Segments | segment			4
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income		$ 173,135	$ 190,588	$ 173,135	$ 174,436
Less: reconciling adjustments		0	0		0
Net Effective Spread		0	0		0
Guarantee and commitment fees		13,666	12,549	13,666	13,976
Other income/(expense)		7,276	3,754		(2,236)
Non-interest income/(loss)		20,942	16,303		11,740
Release of losses		(3,504)	(7,805)	(3,504)	(238)
(Provision)/release of reserve for losses		3	(250)	3	(97)
Noninterest Expense, Excluding Loan, Lease and Other Losses		(51,925)	(61,403)	(51,925)	(49,819)
Non-interest expense		(51,922)	(61,653)		(49,916)
Core earnings before income taxes		138,651	137,433		136,022
Income Tax Expense (Benefit)		(29,105)	(28,785)	(29,105)	(27,942)
Segment core earnings before preferred stock dividends and attribution of income to non-controlling interest - preferred stock dividends		109,546	108,648		108,080
Preferred stock dividends		(13,940)	(17,805)	(13,940)	(13,182)
Loss on retirement of preferred stock		(1,956)	(1,667)	(1,956)	0
Segment core earnings		93,650	89,176		94,898
Assets	$ 24,355,501	21,709,374	24,355,501	21,709,374	18,694,328
On and Off Balance Sheet Program Assets, At Principal Balance	21,924,095	21,117,942	21,924,095	21,117,942	19,724,524
Corporate
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income		11,069	7,201		9,105
Less: reconciling adjustments		(987)	598		(2,047)
Net Effective Spread		10,082	7,799		7,058
Guarantee and commitment fees		0	0		0
Other income/(expense)		166	(536)		(913)
Non-interest income/(loss)		166	(536)		(913)
Release of losses		0	(27)		0
(Provision)/release of reserve for losses		0	0		0
Noninterest Expense, Excluding Loan, Lease and Other Losses		(14,505)	(16,711)		(14,411)
Non-interest expense		(14,505)	(16,711)		(14,411)
Core earnings before income taxes		(4,257)	(9,475)		(8,266)
Income Tax Expense (Benefit)		907	2,066		2,361
Segment core earnings before preferred stock dividends and attribution of income to non-controlling interest - preferred stock dividends		(3,350)	(7,409)		(5,905)
Preferred stock dividends		(13,940)	(17,805)		(13,182)
Loss on retirement of preferred stock	0	0
Segment core earnings		(17,290)	(25,214)		(19,087)
Assets	5,001,865	3,664,823	5,001,865	3,664,823	2,716,994
On and Off Balance Sheet Program Assets, At Principal Balance	0	0	0	0	0
Reconciling Adjustments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income		0	0		0
Less: reconciling adjustments		4,527	(6,368)		23,241
Net Effective Spread		4,527	(6,368)		23,241
Guarantee and commitment fees		(7,669)	(6,601)		(6,756)
Other income/(expense)		5,501	604		(2,747)
Non-interest income/(loss)		(2,168)	(5,997)		(9,503)
Release of losses		0	0		0
(Provision)/release of reserve for losses		0	0		0
Noninterest Expense, Excluding Loan, Lease and Other Losses		0	0		0
Non-interest expense		0	0		0
Core earnings before income taxes		2,359	(12,365)		13,738
Income Tax Expense (Benefit)		(495)	2,596		(2,887)
Segment core earnings before preferred stock dividends and attribution of income to non-controlling interest - preferred stock dividends		1,864	(9,769)		10,851
Preferred stock dividends		0	0		0
Loss on retirement of preferred stock	(1,667)	(1,956)
Segment core earnings		(92)	(11,436)		10,851
Assets	0	0	0	0	0
On and Off Balance Sheet Program Assets, At Principal Balance	0	0	0	0	0
Farm & Ranch
Segment Reporting Information, Profit (Loss) [Abstract]
Release of losses			(2,959)	(3,504)	(238)
(Provision)/release of reserve for losses			(81)	3	(97)
Farm & Ranch | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income		65,098	73,901		62,951
Less: reconciling adjustments		(9,471)	(3,892)		(9,889)
Net Effective Spread		55,627	70,009		53,062
Guarantee and commitment fees		18,593	16,957		17,976
Other income/(expense)		1,397	2,556		1,371
Non-interest income/(loss)		19,990	19,513		19,347
Release of losses		(3,504)	(2,959)		(238)
(Provision)/release of reserve for losses		3	(81)		(97)
Noninterest Expense, Excluding Loan, Lease and Other Losses		(19,375)	(22,414)		(19,026)
Non-interest expense		(19,372)	(22,495)		(19,123)
Core earnings before income taxes		52,741	64,068		53,048
Income Tax Expense (Benefit)		(11,076)	(13,454)		(11,140)
Segment core earnings before preferred stock dividends and attribution of income to non-controlling interest - preferred stock dividends		41,665	50,614		41,908
Preferred stock dividends		0	0		0
Loss on retirement of preferred stock	0	0
Segment core earnings		41,665	50,614		41,908
Assets	6,305,975	5,408,302	6,305,975	5,408,302	4,701,736
On and Off Balance Sheet Program Assets, At Principal Balance	8,581,181	7,776,950	8,581,181	7,776,950	7,233,972
USDA Guarantees | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income		17,470	19,570		20,554
Less: reconciling adjustments		(732)	2,395		(2,499)
Net Effective Spread		16,738	21,965		18,055
Guarantee and commitment fees		958	850		797
Other income/(expense)		174	1,098		20
Non-interest income/(loss)		1,132	1,948		817
Release of losses		0	0		0
(Provision)/release of reserve for losses		0	0		0
Noninterest Expense, Excluding Loan, Lease and Other Losses		(5,757)	(7,270)		(5,309)
Non-interest expense		(5,757)	(7,270)		(5,309)
Core earnings before income taxes		12,113	16,643		13,563
Income Tax Expense (Benefit)		(2,545)	(3,495)		(2,848)
Segment core earnings before preferred stock dividends and attribution of income to non-controlling interest - preferred stock dividends		9,568	13,148		10,715
Preferred stock dividends		0	0		0
Loss on retirement of preferred stock	0	0
Segment core earnings		9,568	13,148		10,715
Assets	2,553,176	2,311,932	2,553,176	2,311,932	2,240,906
On and Off Balance Sheet Program Assets, At Principal Balance	2,786,718	2,620,175	2,786,718	2,620,175	2,515,620
Rural Utilities:
Segment Reporting Information, Profit (Loss) [Abstract]
Release of losses			(4,709)	0	0
(Provision)/release of reserve for losses			(169)	0	0
Rural Utilities: | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income		10,459	21,963		12,505
Less: reconciling adjustments		6,143	2,734		(922)
Net Effective Spread		16,602	24,697		11,583
Guarantee and commitment fees		1,412	1,314		1,599
Other income/(expense)		38	32		33
Non-interest income/(loss)		1,450	1,346		1,632
Release of losses		0	(4,709)		0
(Provision)/release of reserve for losses		0	(169)		0
Noninterest Expense, Excluding Loan, Lease and Other Losses		(3,898)	(6,224)		(3,062)
Non-interest expense		(3,898)	(6,393)		(3,062)
Core earnings before income taxes		14,154	14,941		10,153
Income Tax Expense (Benefit)		(2,972)	(3,137)		(2,133)
Segment core earnings before preferred stock dividends and attribution of income to non-controlling interest - preferred stock dividends		11,182	11,804		8,020
Preferred stock dividends		0	0		0
Loss on retirement of preferred stock	0	0
Segment core earnings		11,182	11,804		8,020
Assets	2,365,996	1,717,405	2,365,996	1,717,405	945,282
On and Off Balance Sheet Program Assets, At Principal Balance	2,816,837	2,280,571	2,816,837	2,280,571	1,592,115
Institutional Credit | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income		69,039	67,953		69,321
Less: reconciling adjustments		520	4,533		(7,884)
Net Effective Spread		69,559	72,486		61,437
Guarantee and commitment fees		372	29		360
Other income/(expense)		0	0		0
Non-interest income/(loss)		372	29		360
Release of losses		0	(110)		0
(Provision)/release of reserve for losses		0	0		0
Noninterest Expense, Excluding Loan, Lease and Other Losses		(8,390)	(8,784)		(8,011)
Non-interest expense		(8,390)	(8,784)		(8,011)
Core earnings before income taxes		61,541	63,621		53,786
Income Tax Expense (Benefit)		(12,924)	(13,361)		(11,295)
Segment core earnings before preferred stock dividends and attribution of income to non-controlling interest - preferred stock dividends		48,617	50,260		42,491
Preferred stock dividends		0	0		0
Loss on retirement of preferred stock	0	0
Segment core earnings		48,617	50,260		42,491
Assets	8,128,489	8,606,912	8,128,489	8,606,912	8,089,410
On and Off Balance Sheet Program Assets, At Principal Balance	$ 7,739,359	$ 8,440,246	$ 7,739,359	$ 8,440,246	$ 8,382,817